Short answer
An onlay is an indirect partial-coverage restoration that covers one or more cusps and preserves the rest of the tooth instead of reducing it for a full crown. In e.max (lithium disilicate) it has ten-year clinical data and needs at least 1.0 mm of clearance; for zirconia, the evidence is still mostly in vitro.
What it is
An indirect partial-coverage restoration that covers one or more cusps of a posterior tooth, designed in CAD on your scan. It replaces only what was lost; sound walls stay where they are.
We make onlays in e.max (lithium disilicate) in our in-house ceramics department, or in monolithic zirconia, milled and sintered. You choose the material on the prescription.
When to prescribe it
An onlay fits when the defect is too large for a direct restoration but there is still tooth worth saving. For e.max, the longest follow-up comes from Malament and colleagues in The Journal of Prosthetic Dentistry: 556 pressed partial coverage restorations, with estimated onlay survival of 98.3% at 9.8 years. All six failures in the study were in molars.
A 2025 systematic review by Prott and colleagues, limited to randomized trials, found 93.7% survival at three years for lithium disilicate. The authors call the long-term performance of partial coverage restorations uncertain. For zirconia, the evidence is mostly in vitro: in a chewing simulator, adhesively bonded 3Y zirconia onlays did not fracture.
How we make it
An e.max onlay is made in our ceramics department; a zirconia onlay is milled in-house, also in São Paulo, Brazil. Both are stained and glazed by hand. Every stage is validated and logged, the onlay goes through eight checks before it ships, and you see its phase in the portal.
What to send
The basics are in our case submission guide. On an onlay the margin runs across the occlusal surface and the proximal boxes, so check that it reads sharply along its whole length, as the intraoral scanning guide shows. If you’re weighing an onlay against a full crown, the e.max crown page covers crown thicknesses.
Frequently asked questions
e.max or zirconia for an onlay?
e.max has the longer clinical track record. In a 10.9-year study in The Journal of Prosthetic Dentistry, estimated survival for lithium disilicate onlays was 98.3%. 3Y zirconia onlays held up to fatigue in a chewing simulator, but long-term clinical data are still missing.
How much occlusal clearance does an e.max onlay need?
Ivoclar specifies a minimum thickness of 1.0 mm for IPS e.max Press onlays. In the in vitro 3Y zirconia study listed below, onlays were also milled at 1 mm occlusal and axial thickness. Keep the margins out of occlusal contact.
How are onlays cemented?
The studies behind onlays used adhesive cementation: acid etching for e.max, and for zirconia, air abrasion with alumina, an MDP-containing primer and a resin cement. The cementation protocol is your call.
Sources
- 10.9-year survival of pressed acid etched monolithic e.max lithium disilicate glass-ceramic partial coverage restorations · The Journal of Prosthetic Dentistry (2021)
- Survival and complications of partial coverage restorations on posterior teeth — a systematic review and meta-analysis · Journal of Esthetic and Restorative Dentistry (2025)
- Monolithic zirconia partial coverage restorations — an in vitro mastication simulation study · Journal of Prosthodontics (2021)
- IPS e.max Press — indications and minimum thicknesses · Ivoclar